Authors

Discussion

Cutaneous leishmaniasis is a neglected tropical disease caused by the intracellular protozoan parasite Leishmania. It is transmitted when female sand flies bite mammalian hosts, such as humans, to obtain a bloodmeal. The disease mainly occurs in tropical and subtropical areas but is spreading to previously unaffected areas. Currently, there are a few antileishmanial drug treatments available, such as antimonials, amphotericin B, miltefosine and paromomycin. However, these drugs have multiple practical shortcomings, their mode of action is unknown or poorly understood, or they face the development of drug resistance. Therefore, it is essential to develop new drugs for the treatment of leishmaniasis. Nucleoside analogues are considered promising alternative drug treatments. Since Leishmania parasites are unable to synthesise their own purines de novo, they rely completely on salvaging purines from the host. This process provides interesting targets for drug discovery of new antileishmanial compounds. In this project, we explored the in vitro and in vivo activity of N⁶-methyltubercidin, also known as CL5564, against L. amazonensis, after it demonstrated potent activity against Trypanosoma cruzi and L. infantum. With selectivity indices of 278 and 43, respectively, CL5564 was 6.5 -fold (p = 0.0002) more potent dan miltefosine, a reference antileishmanial drug, against intracellular amastigote forms in peritoneal mouse macrophages. Combination treatment of CL5564 and miltefosine on ex vivo amastigotes resulted in an additive effect. These results stimulated us to study the activity of CL5564 in a mouse model of cutaneous Leishmania infection: BALB/c female and male mice infected by L. amazonensis and treated with CL5564 (10 mg/kg, intralesional route for five days) presented a >93% reduction of paw lesion size, similar to Milteforan^TM given orally at 40 mg/kg, while the combination (10 + 40 mg/kg of CL5564 and Milteforan^TM, respectively) caused >96% reduction. The qPCR data confirmed the suppression of parasite load after treatment, but only the combination approach reached 66% of parasitological cure. These results warrant additional studies with nucleoside derivatives.